Gas analyzer



Dec. 28, 1954 GAS ANALYZER R. D. RICHARDSON Original Filed May 2, 1947 n FIG. I.

ATTORNEYS GAS AN ALYZER Robert D. Richardson, Michigan City, Ind., assignor to Cambridge Instrument Co. Inc., New York, N. Y., a corporation of New York Original application May 2, 1947, Serial No. 745,418. Divided and this application December 4, 1952, Serial No. 333,981

4 Claims. (Cl. 23-255) This invention relates to gas analysis, and more in particular to the provision of means for use with an internal combustion engine to determine and control the ratio ofthe fuel to the air being supplied to an internal combustion engine, this ratio being referred to as the fuel-air ratio. The illustrative embodiment of the invention is a gas analysis instrument of the same general character as that disclosed in my copending application Serial No.

`595,705 filed May 25, 1945, now U. S. Letters Patent No. 2,633,737, issued April 7, 1953. These instruments are adapted to determine various constituents of gas mixtures and they operate upon the principle of comparing the thermal conductivity of a standard gas sample with that of a sample of the gas under test. Gases differ from one another in their ability to conduct heat and this characteristic is useful in identifying gases and in determining the percentages of certain gases in gas mixtures. For example, considering air as a standard medium, the thermal conductivity of hydrogen is much higher than that of air, whereas the thermal conductivity of carbon dioxide is less than that of air. Thus, if any appreciable amount of hydrogen is present in air, the thermal conductivity of the mixture is relatively high, whereas, *ify carbon dioxide is present the thermal conductivity is lower.

It is an object of the present invention to provide for the measurement and adjustment of the fuel-air ratio of United States Patent() an internal combustion engine with an instrument of the above character. Itis a further object to provide a simplifed and sturdy instrument for carrying out the above.

In the accompanying drawing is shown diagrammatically an apparatus by which these objects are achieved. It should be understood that this drawing and the following description are not intended to be exhaustive or limiting of the invention but on the contrary are chosen for purposes of illustration and with a view to explaining to others skilled in the art the principles of the mventlon as well as the best manner of applying it to practical use and to suggest various modifications so that others skilled in the art will be enabled to alter and modify the structures within the scope of the invention and to embody the invention in numerous forms each as may be best suited to the conditions and requirements of a particular use.

In the drawings:

Figure l is a schematic circuit diagram of one embodiment of the invention; Figure 2 is a schematic showing of the manner of passing the gas through the instrument; and,

Figure 3 is a graph showing the variation in certain of the constituents in the exhaust gases from an internal combustion engine as well as the straight line relationship between the fuel-air ratio and the indication on the instrument scale.

It is desirable to operate an internal combustion engine with only that amount of air which is required for perfect combustion of the fuel being used because either an excess of air or an excess of fuel causes inefficient operation. It has been found that the constituents of the exhaust gases vary in accordance with the fuel-air ratio and, in accordance with the present invention, this ratio is determined by analysis of the exhaust gases. In Figure 3 of the drawings certain of the constituents of the exhaust gases are indicated in percentages throughout the range from a relatively large amount of excess air to a relatively large amount of excess fuel. At the center of the figure 2,698,223 Patented Dec. 28, 1954 ICC is approximately .07; and, at the left is the zone of excess a1r and at the right is the zone of excess fuel.

t The amount of carbon dioxide increases quite steadily 1n the zone of excess air to a maximum value at the zone of perfect combustion, and it then decreases again in the zone of excess fuel. There is no appreciable amount of hydrogen in the zone of excess air and in the zone of perfect combustion, but as the amount of fuel is increased in the zone of excess fuel the amount of hydrogen lncreases steadily. When there is a large amount of excess a1r there is a large amount Vof oxygen, but in the excess fuel zone there is little or no oxygen. Conversely, in the zone of excess air there is little or no carbon monoxide, but in the excess fuel zone the amount of carbon monoxlde increases steadily. Of these gases Vthe thermal conductivity of hydrogen is much greater than that of air, whereas the thermal conductivities of carbon dioxide, carbon monoxide and oxygen are less than that of air. However, the difference between the thermal conductivities of air and carbon dioxide, carbon monoxide and oxygen is smallcompared with the same characteristic for hydrogen. In the illustrative embodiment of the present mvention carbon monoxide and oxygen are ignored and the fuel-air ratio is determined by measuring the amount of carbon dioxide within the excess air zone and the zone of perfect combustion and by measuring the hydrogen and the carbon dioxide in the zone of excess fuel. Thus the instrument provides an indication which results from adding the amount of carbon dioxide to the amount of hydrogen present. Therefore, as the fuel-air ratio is increased within the excess air zone, the scale indication results from the presence of carbon dioxide only because there is no appreciable amount of hydrogen present; as the fuel-air ratio is increased from the zone of perfect combustion into a Zone of excess fuel, the eifect of the increase in the amount of hydrogen is greater than the eifect of the decrease in the amount of carbon dioxide and the instrument is so arranged that a straight line relationship is obtained throughout the operating range.

Referring particularly to Figure l of the drawings, a Wheatstone bridge circuit is formed-by four resistance legs, 2, 4, 6 and 8. A battery 10 is connected between the juncture 12 of legs 2 and 4 and the juncture 14 of legs 6 and S, and a galvanometer 16 is connected between therjuncture 18 of legs 2 and 6 and the juncture 20 of legs 4 and 8. Legs 2 and 6 are identical and form one branch of the bridge which measures the carbon dioxide present, and legs 4 and 8 are identical and form the other branch of the bridge which measures the hydrogen present. The legs are formed by spirals of platinum wire and legs 2, 6 and 8 are exposed to the exhaust gases, whereas leg 4 is sealed in an air-filled tube and thus is Vsurrounded by a standard gas medium.

The legs are positioned as indicated schematically in Figure 2 and the exhaust gases are directed along a hori- Zontal passageway 22. as indicated .by the arrows, past two pockets 24 and 26. Legs 4 and 6 are positioned in the upper portion of pocket 24 and legs 2 and 8 are positioned in the upper portion of pocket 26. The mouth of pocket 26 is filled with a loose mass 27 of soda lime which is a carbon dioxide absorbent, so that the carbon dioxide is adsorbed from the gases which are exposed to legs 2 and 8. The mouth of pocket 24 is filled with an inert material 28 having the same diffusing characteristics as the soda lime 27. Thus, with the exhaust gases flowing along passageway 22 all of the legs are separated from the main stream of the gases by equal diffusion paths. In this way all of the legs are subjected to the influence of the same gas sample; that is, at any instant a change in the constituency of the' exhaust gases affects the constituency of the gases in the two pockets simultaneously.

From the above it is seen that leg 6 is exposed to the exhaust gases after they pass through the diffusion path but without carbon dioxide being removed, Whereas leg 2 is exposed to the exhaust gases after the gases have passed through an identical diffusion path during which the carbon dioxide has been removed.

As indicated above, the thermal conductivity of carbon dioxide is less than that of air and therefore if carbon diioxide isvpresent in the exhaust gases, the cooling eifectof the gases which include carbon dioxide and which sur- Around leg 6 is less than the cooling elect of the gases surrounding leg 2 because the carbon dioxide has been removed from the gases in pocket 26. In this way the presence of carbon dioxide in the exhaust gases causes an increase in the temperature of leg 6 which increases the resistance of this leg and unbalances the bridge. This unbalance gives an indication on galvanometer 16 which has its scale calibrated in accordance with the showing of Figure 3; thus, the fuel-air ratio within the excess air zone and the zone of perfect combustion is indicated in accordance with the amount of the. unbalance of the bridge caused by a rise in the resistance of resistance leg 6 when carbon dioxide is present.

Asindicated above, leg 4 is sealed in a standard gas medium and is positioned with leg 6in pocket 24, whereas leg 8 is positioned in pocket 26 and is surrounded by the carbon dioxide-free exhaust gases. Hydrogen is not absorbed by soda lime 27 and therefore when hydrogen is present in. the exhaust gases it appears in pocket 26. As previously pointed out, hydrogen has a higher thermal conductivity than air so that the presence of hydrogen in pocket 26 causes the cooling effect of the gases surrounding leg 8 to be greater than that of the standard gas me- .dium surrounding leg 4; this decreases the temperature of leg 8 below that of leg 4 so that the resistance of leg 8 is decreased and the bridge is unbalanced. The unbalancing of the bridge caused by the presence of hydrogen is in the same direction and therefore additive to the unbalance caused by the presence of carbon dioxide. Therefore, as shown at the right-hand side of Figure 3, the scale indication within the excess fuel Zone results from the additive effect of the presence of carbon dioxide and. hydrogen. The change in the thermal conductivity of a gas mixture caused by a given percentage of hydrogen causes a much greater change in the thermal conductivity of the gas mixture than does the presence of the same amount of carbon dioxide. However, the two gases are measured independently and the relative values ofthe resistances of the legs of the bridge are so adjusted as to cause the two gases to exert the relative effects desired; that is, in the zone of excess` fuel where the amount of carbon dioxide decreases and the amount of hydrogen increases, the effect of hydrogen is so adjusted that it overcomes the effect of the decrease in carbon dioxide and gives a straight line function to the scale indication. Thus the scale will have fairly evenly spaced markings and accurate indications are obtained throughout the entire range of the scale.

In the illustrative embodiment of the invention it is important that the instrument be extremely accurate inthe zone of perfect combustion so that the fuel-air ratio may be accurately adjustedA within this zone. As pointed out above,r carbon dioxide is present in its maximum amount Within this zone and therefore by relying upon carbon dioxide within this zone to indicate the fuel-air ratio, the desired accuracy is obtained. Furthermore, hydrogen, oxygen, and carbon monoxide are not absorbed by soda lime 27 and the presenceof these gases does not affect the carbon dioxide indication because any effect of these other gases upon the temperature of leg 6 is balanced out by an identical effect upon leg 2.

As various embodiments may be made of the above invention and as changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

This application is a division of application Serial No. 745,418, tiled May 2, 1947, now abandoned.

claim:

l. In an instrument for electrically measuring the ratio of components in a gas sample containing at least two components, one of said components having a thermal conductivity substantially greater than a standard gas and the other component having a thermal conductivity substantially less than said standard gas comprising condnt means to conduct and direct said gas sample from a source to a gas testing apparatus which comprises a first gas testing chamber including inlet means connected to said conduit means, a second gas testing chamber including inlet means connected to said conduit means. said second gas testing chamber being separate from said first gas testing chamber and positioned proximate and adjacent to said first gas testing chamber, each of said chambers being adapted to contain solid material .of substantially equivalent gas flow resistance in their respective. inlets, the solid material positioned in the first testing chamber inlet being substantially inert and the solid material positioned in the second testing chamber inlet being adapted to absorb the component in the gas having a thermal conductivity substantially less than said standard gas, a Wheatstone bridge circuit having a pair of input terminals andv first, second, third, and fourth arms, said rst and second arms compriisng one side of the bridge and being connected in series between said input terminals, said third and fourth arms comprising the other side of the bridge and also being connected in series between said input terminals, an output terminal in said iirst side between said first and second arms, a second output terminal in said second side between said third and fourth arms, and galvanometer means connected between said output terminals, said .rst and fourth arms constituting `diametrically opposed arms in said bridge circuit, located within said second gas testing chamber andl exposed to the gas sample therein, said second and third arms also constituting diametrically opposed arms in said bridge circuit, located within said first gas testing chamber, said fourth arm being exposed to the gas sample therein and means surrounding and enclosing said third arm in a standard reference gas medium.

2. In an instrument for measuring thc fuel-air ratio in an internal combustion engine, the combination of conduit means to conduct and direct exhaust gases from the engine; a pair of exhaust gas-receiving chambers` positioned adjacent tosaid conduit means, each of said chambers having an inlet aperture whereby exhaust gas may pass from said conduit means to said chamber; one of said chambers being adapted to contain a loose body of carbon dioxide absorbent material at a point adjacent to its inlet aperture; the other of said chambers being adapted to contain a loose body of an inert solid material at a point adjacent to its inlet aperture thereby providing a gas flow resistance substantially identical to said loose body of carbon dioxide absorbent; two electrical resistance elements positioned in said first chamber; said resistance elements constituting diametrically opposite sensing arms of a Wheatstone bridge circuit; two additional resistance elements positioned in said second chamber and constituting diametrically opposite sensing arms of said bridge circuit; one of said latter resistance elements being sealed from contact with exhaust gas but being subjected to a standard gas medium; and galvanometer means responsive to relative unbalance between said sensing arms.

3. An instrument for measuring the fuel-air ratio in an internal combustion engine as a function of the carbon monoxide and hydrogen components in exhaust gas from said engine, which comprises conduit means for conducting said exhaust gas` from the engine; a pair of exhaust gas-receiving chambers adjacent to said conduit means; each of said chambers having an inlet aperture communicating with said conduit; each of said chambers also being. adapted to contain a loose body of solid material constituting substantially identical gas ow resistances; said material in a tirst of said chambers being a carbon dioxide absorbent; a pair of electrical resistance elements positioned in said first-named lchamber and responsive to hydrogen components in said exhaust gas; said pair of resistance elements constituting diametrically opposed sensing arms of a four arm Wheatstone bridge circuit; a second pair of electrical resistance elements positioned in the second chamber; one of said latter elements being sealed from contact with exhaust gas but being enclosed. in a standard gas medium; the other of said second pair of elements being exposed to said exhaust gas; said second pair of resistance elements constituting diametrically opposed sensing arms of said bridge circuit; and galvanometer means responsive to relative unbalance between said sensing arms whereby unbalance of said bridge due to said hydrogen components is additive to the unbalance due to said carbon dioxide components.

4. An instrument for electrically measuring the ratio of components in a gas sample containing two components, one of said components having a thermal conductivity substantially greater than a standard gas and the other having a thermal conductivity substantially less than said standard gas which comprises: two separate gas-receiving chamberscommunicating with a source of said. gas sample; each of saidchamhers being adapted'to contain solid material providing inlet flow conduits therein of substantially equivalent gas flow resistance; said solid material in a first of said chambers being adapted to absorb the one of said components in the gas sample having a thermal conductivity substantially less than said standard gas; a pair of electrical resistance elements in one of said chambers and constituting diametrically opposed sensing arms of a four arm Wheatstone bridge circuit; a second pair of electrical resistance elements in the second chamber constituting diametrically opposed sensing arms of said bridge circuit; and galvanometer means positioned in said circuit to measure the electrical unbalance between said sensing arms due to changes in the proportions of components in said gas sample.

Number Date Rodhe Oct. 11, 1927 20 6 Number Name Date 1,681,047 Porter Aug. 14, 1928 2,154,862 Olshevsky Apr. 18, 1939 2,255,551 Willenborg Sept. 9, 1941 2,298,288 Gerrish et al Oct, 13, 1942 2,533,339 Willenborg Dec. 12, 195) 2,585,959 Minter Feb. 19, 1952 2,596,992 Fleming May 20, 1952 2,618,150 Willenborg Nov. 18, 1952 2,633,737 Richardson Apr. 7, 1953 FOREIGN PATENTS Number Country Date 373,239 Germany Apr. 9, 1923 OTHER REFERENCES Daynes: Gas Analysis by Measurement of Thermal Conductivity, pages 182-194, 232-235, 316-319 (1933). Pub. by Cambridge, at the University Press, England. 

4. AN INSTRUMENT FOR ELECTRICALLY MEASURING THE RATIO OF COMPONENTS IN A GAS SAMPLE CONTAINING TWO COMPONENTS, ONE OF SAID COMPONENTS HAVING A THERMAL CONDUCTIVELY SUBSTANTIALLY GREATER THAN A STANDARD GAS AND THE OTHER HAVING A THERMAL CONDUCTIVITY SUBSTANTIALLY LESS THAN SAID STANDARD GAS WHICH COMPRISES: TWO SEPARATE GAS-RECEIVING CHAMBERS COMMUNICATING WITH A SOURCE OF SAID GAS SAMPLE: EACH OF SAID CHAMBERS BEING ADAPTED TO CONTAIN SOLID MATERIAL PROVIDING INLET FLOW CONDUITS THEREIN OF SUBSTANTIALLY EQUIVALENT GAS FLOW RESISTANCE; SAID SOLID MATERIAL IN A FIRST OF SAID CHAMBERS BEING ADAPTED TO ABSORB THE ONE OF SAID COMPONENTS IN THE GAS SAMPLE HAVING A THERMAL CONDUCTIVITY SUBSTANTIALLY LESS THAN SAID STANDARD GAS; A PAIR OF ELECTRICAL RESISTANCE ELEMENTS IN ONE OF SAID CHAMBERS AND CONSTITUTING DIAMETRICALLY OPPOSES SENSING ARMS OF A FOUR ARM WHEATSTONE BRIDGE CIRCUIT; A SECOND CHAMBER CONSTITUTING DIAMETRICALLY OPPOSED THE SECOND CHAMBER CONSTITUTING DIAMETRICALLY OPPOSED SENSING ARMS OF SAID BRIDGE CIRCUIT; AND GALVANOMETER MEANS POSITIONED IN SAID CIRCUIT TO MEASURE THE ELECTRICAL UNBALANCE BETWEEN SAID SENSING ARMS DUE TO/CHANGES IN THE PROPORTIONS OF COMPONENTS IN SAID GAS SAMPLE. 